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Old 21st November 2009, 05:22 PM   #1
pointy is offline pointy  United Kingdom
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Default transformer coupled plate follower

transformer coupled plate follower

short and sweet................... can i use small wall wart transformers back to back
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Old 21st November 2009, 05:27 PM   #2
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Quote:
Originally Posted by pointy View Post
transformer coupled plate follower

short and sweet................... can i use small wall wart transformers back to back
For what?

I don't like them for power, and as a substitute for an OPT it would be far worse, twice the leakage inductance, core loss, stray capacitance, etc.

You really ought to consider a proper plate to line or interstage transformer. Alternately a small power toroid might work in a CCS loaded parafeed arrangement. I would use one with a low step down ratio if you need gain. Not guaranteed to work and you should use a tube with really low rp as well.

Shoog might have some further insights.
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Old 21st November 2009, 05:37 PM   #3
pointy is offline pointy  United Kingdom
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for what.....!

its for a big box try everything pre-amp project ive been sticking together

thd and sound quality are not the issue

its just a big box with switches on the front so i can try out every thing inside it...........
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Old 21st November 2009, 07:47 PM   #4
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What do you mean by a "plate follower"? Being a Brit you ought to use the word "anode". Do you mean an amplifying stage in which the output from the anode is fed back to the grid, which is the proper usage of the phrase ; or do you mean a common cathode stage which doesn't have this connection?
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Old 21st November 2009, 07:58 PM   #5
pointy is offline pointy  United Kingdom
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yowww......barretter

http://www.glass-ware.com/tubecad/PF4.gif

as always i hope the link works

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Old 21st November 2009, 08:41 PM   #6
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"Yowww"? What does that mean? I speak several languages but that doesn't appear in any of them. I have no idea whether a wall-wart would work in that position or not, but then I've never followed the fashion for using transformers everywhere. I can remember when colleagues in my DIY audio circle assured me that using inductors in my power supplies would "slow" everything down. Then, a year later, they had chokes everywhere, followed by an unshakeable belief in transformer-tapped volume controls a bit later.
As you seem fairly gung-ho why noyt just try it?
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Old 21st November 2009, 08:43 PM   #7
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Using back to backs will multiply an already high interwinding capacitance nanoFarads aught to be expected.
Toroidals as a step down parafeed will work and sound fine. As a stepup for extra gain don't expect anything but terribly rolled off highs. I went off parafeed due to the limitations of the parafeed cap.

Shoog
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Old 21st November 2009, 09:04 PM   #8
pointy is offline pointy  United Kingdom
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yes..........they stopped using transformer inversion in the 20s, but started to use interstage again in the 70s.

as you say gun ho so I think I will try to by pass the transformers with a cap and some resistor when I try it out.

PS it is a safe pre-amp metal RF skinned with a ply with sleeve, all switches have long spindles, make before break up rated etc etc.................

so I will be trying just about everything that can go in it.
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Old 21st November 2009, 10:47 PM   #9
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OK, but WTF do you want a "Plate follower" for anyway? Didn't TubeCAD explain what it's for? A tube and a transformer to get zero gain and what...? Seems a COMPLETE waste of time and money!

Regards, Allen
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Old 21st November 2009, 11:26 PM   #10
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Well you can have some gain with an anode follower depending on the ratio of the feedback to the input resistor but I have no idea what the Tubecad circuit is supposed to achieve. I've only seen detailed discussion of anode followers in radio circuit books much like the real "grounded grid" circuit (NOT the misnamed Rozenblit version of the cathode -coupled amplifier).
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